1. Field of the Invention
The present invention is related to a display apparatus. More particularly, the present invention is related to a display apparatus displaying pseudo gray levels or shades and method for displaying the same.
2. Description of the Related Art
A large number of gray levels are requested for improving the quality of pictures displayed by display devices, such as an LCD (Liquid Crystal Display) and a PDP (Plasma Display Panel). However, the limited number of gray levels are available in such display devices.
A pseudo gray level method is often used for increasing the number of displayable gray levels. The pseudo gray level method generates an m-bit gray level signal from an original n-bit gray level signal (n being larger than m) to enable the display which can physically display 2m gray levels to display 2n gray levels in appearance.
A pseudo gray level processor for implementing the pseudo gray level method is disclosed by Matsunaga et al. in Japanese Laid Open Patent Application (JP-A-Heisei 9-90902). The conventional pseudo gray level processor implements the error diffusion method for displaying pseudo gray levels. The conventional pseudo gray level processor is provided with a one-dot delay circuit 151, a first adder 152, an error diffusion calculating circuit 156 and a an initial value setting circuit 170, as shown in FIG. 1. The error diffusion calculating circuit 156 is composed of a second adder 158, a one-dot delay circuit 160, a switching circuit 162, a calculation control circuit 164 and a threshold setting circuit 168. The initial value setting circuit 170 is composed of an initial value setting ROM 172, a line counter 174 and a frame counter 176.
The error diffusion calculating circuit 156 carries out an error diffusion calculation on the basis of a lower bit data A which is lower (nxe2x88x92m) bits of an n-bit (for example, 8-bit) input picture data. The calculation control circuit 164 calculates a value xcex4 by
xcex4=Dxe2x88x92S,
where D is a value sent from the one-dot delay circuit 160, and S is a threshold sent from the threshold setting circuit 168. Then the calculation control circuit 164 sends xe2x80x9c1xe2x80x9d as a carry value E to the first adder 152 when the value xcex4 is 0 or more.
The first adder 152 adds the carry value E and data B that is upper m bits (for example, 5 bits) of the picture signal to generate a pseudo gray level data F. The first adder 152 outputs the pseudo gray level data F to a display panel.
The initial value setting circuit 170 sends an initial value of the error diffusion calculating circuit 156. The initial value is different for each line of the display panel to erase the directivity of a diffusion pattern. Moreover, the pseudo gray level processor does not require a line memory for each line of the display panel.
However, the number of gray levels that can be represented by the pseudo gray level data F is smaller than the number of gray levels that can be represented by an input picture data A. The reason is as follows. If all the upper m bits of the input picture data A are xe2x80x9c1xe2x80x9d, all the bits of the pseudo gray level data F are xe2x80x9c1xe2x80x9d for any values of the lower bits (nxe2x88x92m) of the input picture data A. The number of gray level in which the upper m bits are all xe2x80x9c1xe2x80x9d is 2(nxe2x88x92m). When the input picture data representative of any of the 2(nxe2x88x92m) gray levels is inputted, the pseudo gray level data F have the value in which all the bits are xe2x80x9c1xe2x80x9d. Therefore, the pseudo gray level data F can represent only 2nxe2x88x922(nxe2x88x92m)+1 gray levels. The pseudo gray level processor desirably allows the pseudo gray level data of m bits to represent all the 2n gray levels for n larger than m.
Frame rate control is another typical technique for increasing displayable gray levels. A frame rate control method is disclosed by Miyatake in Japanese Laid Open Patent Application (Jp-A-Heisei 7-120725). Miyatake describes a method for driving a LCD in which a gray level signal applied to an LCD pixel is switched every frame and has different signs and effective voltages for former n frames and latter n frames of successive 2n frames.
Still another technique which may be related to the present invention is disclosed by Furuhashi et al. in Japanese Laid Open Patent Application (Jp-A-Heisei 9-106267). Furuhashi et al. disclose an LCD for increasing contrast. One electrode of each LCD pixel is a drive electrode driven by a LCD driver, and another is a common plate electrode. The LCD includes a plate electrode driver for driving the plate electrode. The plate electrode driver latches the upper bits of the gray level data, and outputs one of predetermined voltages in response to the upper bits. The plate electrode driver allows the LCD pixels to be applied with a voltage larger than a dynamic range of the LCD driver, and increase the contrast of the LCD. However, Furuhashi et al. does not describe the pseudo gray levels.
Therefore, the object of the present invention is to provide an improved method for displaying pseudo gray levels.
More particularly, the object of the present invention is to provide a pseudo gray level processor which allows the pseudo gray level data of m bits to represent all the 2n gray levels for n larger than m.
Another object of the present invention is to provide a pseudo gray level processor for generating an m-bit pseudo gray level signal from an n-bit input gray level signal (n being larger than m) such that a fixed pattern is hard to be induced in a picture displayed by a display apparatus.
In order to achieve an aspect of the present invention, a display apparatus is composed of a pseudo gray level data processor. The pseudo gray level data processor generates pseudo gray level data having m bits based on input gray level data having n bits representative of an input gray level of 2n gray levels, where n is a natural number equal to or more than 2, and m is a natural number less than n. The pseudo gray level data processor includes a state variable generator, an adder and a pseudo gray level data generator. The state variable generator generates a state variable data having nxe2x88x92m bit(s) on the basis of lower nxe2x88x92m bit(s) of the input gray level data. The adder calculates a sum of the lower nxe2x88x92m bit(s) of the input gray level data and the state variable data, and outputs a carry bit representative of carry-over of the sum. The pseudo gray level data generator generates the pseudo gray level data based on the input gray level data and the carry bit. In a first case when the carry bit is xe2x80x9c0xe2x80x9d and the input gray level belongs to first gray levels of the 2n gray levels, the pseudo gray level data generator defines the pseudo gray level data such that the pseudo gray level data equals upper m bits of the input gray level data in a first case. In a second case when the carry bit is xe2x80x9c1xe2x80x9d and the input gray level data belongs to the first gray levels, the pseudo gray level data generator defines the pseudo gray level data such that upper mxe2x88x921 bit(s) of the pseudo gray level data equals upper mxe2x88x921 bit(s) of the input gray level data and the LSB (least significant bit) of the pseudo gray level data is selected from xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d.
It is desirable that upper mxe2x88x921 bit(s) of the input gray level data are xe2x80x9c1xe2x80x9d and the m-th significant bit of the input gray level data is xe2x80x9c0xe2x80x9d when the input gray level data represents any one of the first gray levels.
In addition, a first probability of the LSB of the pseudo gray level data being xe2x80x9c0xe2x80x9d in the second case substantially equals a second probability of the LSB of the pseudo gray level data being xe2x80x9c1xe2x80x9d in the second case.
When the display apparatus further includes a pixel matrix unit including pixels displaying a displaying gray level indicated by the pseudo gray level data, the pseudo gray level data generator preferably determines the LSB of the pseudo gray level data in response to a position of the pixels in the pixel matrix unit.
When the pixels includes first and second pixels, the first pixels displaying a first displaying gray level indicated by the pseudo gray level data having the LSB of xe2x80x9c1xe2x80x9d in the second case, the second pixels displaying a second displaying gray level indicated by the pseudo gray level data having the LSB of xe2x80x9c0xe2x80x9d in the second case, and the pixel matrix unit includes a first area in which the first pixels are located and a second area in which the second pixels are located, it is desirable that the first and second area are alternately located in the pixel matrix unit.
It is also desirable that the pseudo gray level data generator defines the gray level data such that the pseudo gray level data equals upper m bits of the input gray level data in a third case when the carry bit is xe2x80x9c1xe2x80x9d and the input gray level belongs to second gray levels of the 2n gray levels other than the first gray levels, and such that upper mxe2x88x921 bits of the pseudo gray level data equals upper mxe2x88x921 bits of the input gray level data and the LSB of the pseudo gray level data is selected from xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d in a fourth case when the carry bit is xe2x80x9c0xe2x80x9d and the input gray level data belongs to the second gray levels.
In this case, it is desirable that upper m bits of the input gray level data are xe2x80x9c1xe2x80x9d and at least one of lower nxe2x88x92m bits of the input gray level data is xe2x80x9c0xe2x80x9d when the input gray level data represents any one of the second gray levels.
Furthermore, a third probability of the LSB of the pseudo gray level data being xe2x80x9c0xe2x80x9d in the fourth case is preferably substantially equal to a fourth probability of the LSB of the pseudo gray level data being xe2x80x9c1xe2x80x9d in the fourth case.
The pseudo gray level data generator preferably defines the pseudo gray level data such that the pseudo gray level data equals a sum of the carry bit and upper m bits of the input gray level data in a fifth case when the input gray level does not belong to any of the first and second gray levels.
The state variant data are preferably defined by
x(1)=xINI, and
x(i)=uL(ixe2x88x921)+x(ixe2x88x921)(ixe2x89xa72),
where i is a natural number, u(i) is one of the input gray level data which is i-th inputted to the pseudo gray level data processor, uL(i) are lower n-m bits of u(i), x(i) is one of the state variant data which is produced in response to u(i), and xINI is a predetermined value.
In order to achieve another aspect of the present invention, a display apparatus is composed of a pseudo gray level data processor generating pseudo gray level data having m bits based on input gray level data having n bits representative of an input gray level of 2n gray levels, n being a natural number equal to or more than 2, and m being a natural number less than n. The pseudo gray level data processor includes a state variable generator, an adder, and a pseudo gray level generator. The state variable generator generates a state variable data having nxe2x88x92m bits, based on lower nxe2x88x92m bits of the input gray level data. The adder calculates a sum of the lower nxe2x88x92m bits of the input gray level data and the state variable data to output a carry bit representative of carry-over of the sum. The pseudo gray level data generator generates the pseudo gray level data based on the input gray level data and the carry bit. In a third case when the carry bit is xe2x80x9c1xe2x80x9d and the input gray level belongs to second gray levels of the 2n gray levels, the pseudo gray level data generator defines the pseudo gray level data such that the pseudo gray level data equals upper m bits of the input gray level data. In a fourth case when the carry bit is xe2x80x9c0xe2x80x9d and the input gray level data belongs to the second gray levels, the pseudo gray level data generator defines the pseudo gray level data such that upper mxe2x88x921 bits of the pseudo gray level data equals upper mxe2x88x921 bits of the input gray level data and the LSB (least significant bit) of the pseudo gray level data is selected from xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d.
In order to achieve still another aspect of the present invention, a display apparatus is composed of a pseudo gray level data processor generating pseudo gray level data having m bits based on input gray level data having n bits representative of an input gray level of 2n gray levels, n being a natural number equal to or more than 2, and m being a natural number less than n. The pseudo gray level data processor includes a state variable generator, a subtracter, and a pseudo gray level data generator. The state variable generator generates a state variable data having nxe2x88x92m bits, based on lower nxe2x88x92m bits of the input gray level data. The subtracter calculates the difference the lower nxe2x88x92m bits of the input gray level data minus and the state variable data to output a carry bit representative of carry-over of the difference. The pseudo gray level data generator generates the pseudo gray level data based on the input gray level data and the carry bit. In a first case when the carry bit is xe2x80x9c0xe2x80x9d and the input gray level belongs to first gray levels of the 2n gray levels, the pseudo gray level data generator defines the pseudo gray level data such that the pseudo gray level data equals upper m bits of the input gray level data. In a second case when the carry bit is xe2x80x9c1xe2x80x9d and the input gray level data belongs to the first gray levels, the pseudo gray level data generator defines the pseudo gray level data such that upper mxe2x88x921 bits of the pseudo gray level data equals upper mxe2x88x921 bits of the input gray level data and LSB (least significant bit) of the pseudo gray level data is selected from xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d.
It is desirable that the pseudo gray level data generator defines the gray level data such that the pseudo gray level data equals upper m bits of the input gray level data in a third case when the carry bit is xe2x80x9c1xe2x80x9d and the input gray level belongs to second gray levels of the 2n gray levels other than the first gray levels, and such that upper mxe2x88x921 bits of the pseudo gray level data equals upper mxe2x88x921 bits of the input gray level data and the LSB of the pseudo gray level data is selected from xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d in a fourth case when the carry bit is xe2x80x9c0xe2x80x9d and the input gray level data belongs to the second gray levels.
The pseudo gray level data generator preferably defines the pseudo gray level data such that the pseudo gray level data equals a difference upper m bits of the input gray level data minus the carry bit in a fifth case when the input gray level does not belong to any of the first and second gray levels.
The state variable data are preferably defined by
x(1)=xINI, and
x(i)=uL(ixe2x88x921)+x(ixe2x88x921)(ixe2x89xa72),
where i is a natural number, u(i) is one of the input gray level data which is i-th inputted to the pseudo gray level data processor, uL(i) are lower n-m bits of u(i), x(i) is one of the state variant data which is produced in response to u(i), and xINI is a predetermined value.
In order to achieve still another aspect of the present invention, a display apparatus is composed of a pseudo gray level data processor generating pseudo gray level data having m bits based on input gray level data having n bits representative of an input gray level of 2n gray levels, n being a natural number equal to or more than 2, and m being a natural number less than n. The pseudo gray level data processor includes a state variable generator, a subtracter, and a pseudo gray level generator. The state variable generator generates a state variable data having nxe2x88x92m bits, based on lower nxe2x88x92m bits of the input gray level data. The subtracter calculates a difference the lower nxe2x88x92m bits of the input gray level data minus the state variable data to output a carry bit representative of carry-over of the difference. The pseudo gray level data generator generating the pseudo gray level data on the basis of the input gray level data and the carry bit. In a third case when the carry bit is xe2x80x9c1xe2x80x9d and the input gray level belongs to second gray levels of the 2n gray levels, the pseudo gray level data generator defines the pseudo gray level data such that the pseudo gray level data equals upper m bits of the input gray level data. In a fourth case when the carry bit is xe2x80x9c0xe2x80x9d and the input gray level data belongs to the second gray levels, the pseudo gray level data generator defines the pseudo gray level data such that upper mxe2x88x921 bits of the pseudo gray level data equals upper mxe2x88x921 bits of the input gray level data and LSB (least significant bit) of the pseudo gray level data is selected from xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d.
In order to achieve still another aspect of the present invention, a method of generating pseudo gray level data representative of pseudo gray level is composed of:
sequentially inputting input gray level data, each of which has n bits and is representative of an input gray level of 2n gray levels, n being a natural number equal to or more than 2, and
sequentially generating pseudo gray level data having m bits based on the input gray level data, m being a natural number less than n. The sequentially generating includes:
delaying work data having nxe2x88x92m bits by a duration substantially equal to a temporal interval at which the input gray level data is inputted to output state variable data,
calculating a sum of lower nxe2x88x92m bits of the input gray level data and the state variable data,
outputting the sum as the work data,
outputting a carry bit of the sum,
defining the pseudo gray level data such that the pseudo gray level data equals upper m bits of the input gray level data in a first case when the carry bit is xe2x80x9c0xe2x80x9d and the input gray level belongs to first gray levels of the 2n gray levels, and
defining the pseudo gray level data such that upper mxe2x88x921 bits of the pseudo gray level data equals upper mxe2x88x921 bits of the input gray level data and LSB of the pseudo gray level data is selected from xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d in a second case when the carry bit is xe2x80x9c1xe2x80x9d and the input gray level data belongs to the first gray levels.
In order to achieve still another aspect of the present invention, a method of generating pseudo gray level data representative of pseudo gray level comprises:
sequentially inputting input gray level data, each of which has n bits and is representative of an input gray level of 2n gray levels, n being a natural number equal to or more than 2, and
sequentially generating pseudo gray level data having m bits based on the input gray level data, m being a natural number less than n. The sequentially generating includes:
delaying work data having nxe2x88x92m bits by a duration substantially equal to a temporal interval at which the input gray level data is inputted to output state variable data,
calculating a difference lower nxe2x88x92m bits of the input gray level data minus the state variable data,
outputting the difference as the work data,
outputting a carry bit of the difference,
defining the pseudo gray level data such that the pseudo gray level data equals upper m bits of the input gray level data in a first case when the carry bit is xe2x80x9c0xe2x80x9d and the input gray level belongs to first gray levels of the 2n gray levels, and
defining the pseudo gray level data such that upper mxe2x88x921 bits of the pseudo gray level data equals upper mxe2x88x921 bits of the input gray level data and LSB (least significant bit) of the pseudo gray level data is selected from xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d in a second case when the carry bit is xe2x80x9c1xe2x80x9d and the input gray level data belongs to the first gray levels.